Don't attempt parsing falsy datetime values

declaration/fields.py

@@ -69,18 +69,27 @@ def encode(self, value):
 class DateTimeField(GenericField):
 
     def parse(self, value):
+        if not value:
+            return value
+
         if not isinstance(value, datetime.datetime):
             value = parser.parse(value)
 
         return value
 
     def encode(self, value):
+        if not value:
+            return value
+
         return value.strftime("%Y-%m-%dT%H:%M:%SZ")
 
 
 class DateField(DateTimeField):
 
     def parse(self, value):
+        if not value:
+            return value
+
         if isinstance(value, six.string_types):
             value = parser.parse(value)
 
@@ -93,6 +102,9 @@ def parse(self, value):
 class TimeField(DateTimeField):
 
     def parse(self, value):
+        if not value:
+            return value
+
         if isinstance(value, datetime.datetime):
             value = value.time()
 

declaration/tests/test_fields.py

@@ -69,6 +69,25 @@ def test_time_field_trims_excess_from_date_time(self):
         date_value = datetime.datetime(2013, 7, 31, 1, 33, 10)
         assert date_value.time() == field.parse(date_value)
 
+    def test_date_time_fields_ignore_missing_values(self):
+        field = fields.DateTimeField()
+        assert field.parse("") == ""
+        assert field.parse(None) is None
+        assert field.encode("") == ""
+        assert field.encode(None) is None
+
+        field = fields.DateField()
+        assert field.parse("") == ""
+        assert field.parse(None) is None
+        assert field.encode("") == ""
+        assert field.encode(None) is None
+
+        field = fields.TimeField()
+        assert field.parse("") == ""
+        assert field.parse(None) is None
+        assert field.encode("") == ""
+        assert field.encode(None) is None
+
     def test_uuid_field_converts(self):
         field = fields.UUIDField()
         value = "c3864285-1f1e-4c0c-bd95-ad5a8dbf3232"

setup.py

@@ -21,7 +21,7 @@
     author='Jordan Ambra',
     author_email='jordan@serenitysoftware.io',
     url='https://github.com/boomletsgo/declaration',
-    version='0.2.3',
+    version='0.2.4',
     classifiers=classifiers,
     description='Base classes and fields for declarative programming, like Django ORM',
     keywords='declarative declaration metaclass',